1. Field of the Invention
The present invention relates to an optical sensor and an image forming apparatus that incorporates the optical sensor.
2. Discussion of the Background Art
Conventionally, an image forming apparatus is known that executes image quality adjustment control, such as process control, etc., under certain predetermined conditions, such as immediately after power is supplied, a total number of printed sheets reaches a prescribed level, etc.
In such image quality adjustment control involves, for example, a light emitted from a light emitting element of an optical sensor is reflected by a background of a surface of an intermediate transfer belt that serves as a detection object and an image bearer. A light receiving element of the optical sensor then receives the reflection light and outputs a voltage signal in accordance therewith.
Then, a reference toner image having a prescribed shape is formed on a surface of a photoconductor as a detection object and is transferred onto an intermediate transfer belt. Light is emitted from the light emitting element and is reflected by the reference toner image, and such reflection light is received by the light receiving element, so that a corresponding signal (voltage) is outputted in accordance with a reflection light. Then, using the above-mentioned output signal obtained from the background of the surface of the intermediate transfer belt, as a reference, the above-mentioned output signal of the reference toner image is compared to the reference, to ascertain, an amount of attracted toner per unit area of the reference toner image. Based on the thus-obtained tonner attraction amount, an image formation condition as a control target, including but is not limited to a uniform charge voltage, a developing bias, an intensity of optical writing onto a photoconductor, and a toner density of developer, etc., is adjusted so as to keep the attracted toner amount within a prescribed level. By executing the above-mentioned image quality adjustment control, a printing output with a stable consistent image density can be obtained for a considerable period of time.
For the optical sensor, one employing a surface mounting type in which light emitting and light receiving elements are mounted on a surface of a substrate is known as described in Japanese Patent Application Laid Open No. 2005-91252. Specifically, in such an optical sensor, light emitted from the light emitting element in rays parallel to the substrate and reaches the intermediate transfer belt. The light is then reflected in rays parallel to the substrate and is detected by the light receiving element.
Such an optical sensor includes a regular reflection light receiving element that detects a light emitted and regularly reflected by the intermediate transfer belt. In general, an output value of the regular reflection light receiving element of the optical sensor decreases over time due to a change in gloss of the intermediate transfer belt or the like. Thus, correction processing is applied the output value to increase a light intensity of the light emitting element by increasing an input current to be inputted thereto, for example before image adjustment control, so that the output value of the regular reflection light receiving element becomes a prescribed level when the light reaches the intermediate transfer belt. Since the light emitting element is likely damaged when the input current inputted to the light emitting element is excessively increased, a prescribed upper limit of the input current is designated. When the input current required to attain the prescribed level exceeds the prescribed upper limit, the intermediate transfer belt or the like is replaced.
Further, an output of a regular light receiving element of the optical sensor sometimes decreases and does not reach a prescribed level thereof due to variation in an attachment position thereof with regard to an apparatus even in an early stage for reasons as described below.
Specifically, when a reference toner image formed on a belt, such as the intermediate transfer belt is to be detected, rippling of the belt causes inaccurate detection. Thus, the optical sensor is arranged facing a section of the belt winding around a stretching roller. Consequently, a light is emitted from the optical sensor to a curved surface of the belt. Similarly, when a reference toner image on a surface of a drum type photoconductor is detected, a light is also emitted from the optical sensor to a curved belt surface.
In this way, inaccurate attachment of the optical sensor to the apparatus decreases an output of the regular reflection light receiving element as described with reference to FIG. 25.
Specifically, as shown by a solid line in FIG. 25, when a light is emitted onto a curved surface of a detection object 200, an optical sensor is attached determining an attachment angle so that the optical axis is perpendicular to a tangent line through an emission point D1, where light of the detection object 200 is emitted, when viewed from a axial direction.
However, when the attachment position of the optical sensor deviates as shown by a broken line in FIG. 25, the emission point on the detection object 200 is shifted to a point D2, thereby loosing the 90-degree angle of the optical axis to the tangential line contacting an emission point D2. As a result, a regular reflected light strikes the light receiving element at a position deviated from a center on a light receiving surface of the regular reflection light receiving element, and accordingly, a light intensity entering thereto and an output value therefrom decrease.
Consequently, the output value of the regular reflection light receiving element is initially corrected to be a prescribed level, for example before a product is shipped, by increasing the light intensity of the light emitting element. However, when the light intensity is increased by the initial correction before shipping, an input current inputted to the optical element quickly reaches its upper limit. Accordingly, it is important to minimize inaccurate attachment of the optical sensor to the apparatus, and to keep the input current inputted to the light emitting element in an early usage stage as low as possible.
When a surface mounting type element is employed in the above-mentioned light emitting and light receiving elements of the optical sensor, a surface opposite the mounting surface of a substrate on which these light emitting and light receiving elements are mounted, serves as a positioning reference surface.
Inaccurate attachment of the optical sensor to the apparatus is suppressed by tightly contacting the reference surface to an optical sensor mounting member.
However, even if the optical sensor is precisely attached to the apparatus body, a light emission position sometimes deviates due to defective parts precision of the optical sensor itself, thereby sometimes decreasing an output value of the regular reflection light receiving element. Such defective precision of parts can be caused by imprecise mounting of the light emitting and light receiving elements onto the surface of the substrate, as well as variations in the thickness of the substrate itself.
Deterioration in the output of the regular reflection light receiving element caused by dimensional variation of in the parts of the optical sensor themselves can be suppressed to a certain degree if inaccurate mounting of the light emitting and light receiving elements onto the surface of the substrate and variation in the thickness thereof are inspected in an inspection step of the optical sensor, and only those optical sensors passing the inspection are deployed.
However, since only those optical sensors which, when attached to an apparatus, all of attachment errors of light emitting and light receiving elements in relation to the substrate and thickness error of the substrate fall within prescribed tolerances, respectively, a yield percentage is low, thereby increasing the cost.
Further, Japanese Patent Application Laid Open No. 2008-185848 (JP-2008-185848-A) describes an image forming apparatus that includes a moving device for moving an optical sensor to adjust a position thereof. Specifically, even if an incident angle and an emission position of a light with regard to a surface of a detection object deviate due to variation in the optical sensor itself, these deviations are corrected by adjusting the position of the optical sensor, so that decreasing in an output value of a regular reflection light receiving element can be suppressed. As a result, a yield percentage can be improved, restraining production cost increases.
However, in the image forming apparatus of JP-2008-185848-A, a driving device such as motor, etc., is necessitated to move the optical sensor, thereby likely increasing the number of parts and the size of the light emitting and receiving elements as well.